A lock mechanism has at least one tumbler pin having one or more slots in the tip surface of the pin and a key blade which is formed with a projection extending from the surface of the bitting area. The tumbler pin can be rotatable in such a manner that it will seek to accommodate the projection on the surface of the key and to match the surfaces of the key and tumbler pin tip, thus aligning the tumbler pin at a position predetermined by the key bitting. In this regard, the tumbler pin tip is preferably tapered and adapted to engage with a key having a complementarily shaped bitting surface, i.e., complementary to the tapered surface of the tumbler pin tip, such that the tumbler pin will seek to accommodate the tapered surface of the key bitting to align the tumbler pin at a proper position. Alternatively, the tumbler pin can include a projection or the like to inhibit rotation of the tumbler pin. Cylinders and keys according to the present invention can be arranged in hierarchical systems to perform special functions and provide master keying capability.

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